Carding engines comprise a feed roller cooperating with a feed pate to provide a supply of material. A toothed takerin takes the material from the feed plate and transfers it to a toothed main carding cylinder. A series of flats, which may be movable or stationary, cooperate with an arc of the carding cylinder, the flats having carding elements confronting the teeth on the cading cylinder so that a carding action is performed between the flats and the cylinder. After such carding, the resulting fibrous web is taken from the main carding cylinder by a toothed doffer, and is then removed from the doffer by a stripper, from which the web is taken to be fed from the carding engine.
The action of the carding engine is to remove waste material from the feed stock and also to align the usable fibres of the feed stock and also to align the usable main carding action is performed between the flats and the main carding cylinder, carding and cleaning action also occurs on the takerin and in other areas of the main carding cylinder, and particular elements may be associated with either of theses toothed members to enhance the cleaning or straightening effect.
The rotary members of the carding engine rotate at high speed and substantial air currents are generated during operation. Control of these air currents is important to the efficiency of the carding operation, particularly the effective use of air in loosening and removing waste from the fibre without also removing significant quantities of usable fibre, and in extracting the waste from the machine. Various forms if cover for the toothed members are known that can assist in controlling the air flow.
For example, EP-A-0019455 discloses covering that arc of the main carding cylinder which extends from the flats to the doffer with a cover that includes a restriction affecting air pressure in the region where the flats leave the cylinder. The amount of material removed by the flats and taken therefrom as flat strips can be subjected to a degree of control in this way.
GB-B-1483291 discloses a carding engine having a cover over that arc of the main cylinder that extends from the carding means to the doffer, the cover including a plate portion that has a leading edge positioned closely spaced from the trailing edge of the carding means to define a passageway. The combination of centripetal force and induced air flow through the passageway allows trash particles to be thrown from the cylinder and through the passageway, an effect enhanced by a sharpened leading edge of the plate portion.
The present invention seeks to control air flow and trash removal in a novel manner, with the intention of improving the cleaning efficiency of a carding engine, at least when running with some feedstocks. Even small improvements in card cleaning efficiency are of significance in forming silver of better quality.